This invention pertains to magnetic trip solenoids, and more particularly to a cased type rotary or linear solenoid which is magnetically self-holding in an actuated position.
Permanent magnet arrangements have been applied to various open frame type linear type solenoids for the purpose of retaining a solenoid armature or plunger in one of its two positions, normally at the energized position. The permanent magnets hold the armature in such an energized position following the removal of the electric power to the coil. Such trip solenoids are then released by applying a reverse pulse, of limited duration, to the energizing coil to cancel the holding flux, and release the armature for return under the influence of a conventional return spring to the unenergized position. An example of an axial magnetic trip solenoid may be found in my copending application Ser. No. 471,542 filed March 2, 1983.
A highly successful form of solenoid is the cased solenoid. One form of a cased solenoid is a rotary solenoid which employs complementary inclined ball races between relatively moving parts to convert an axial stroke to a rotary stroke, as shown for example in the patents of G. H. Leland, U.S. Pat. No. 2,496,880 of Feb. 7, 1950 and U.S. Pat. No. 2,566,571 of Sept. 4, 1951. In another form, the balls and ball races are omitted, and the solenoid performs only an axial stroke and is known as a linear or push/pull solenoid.
Various arrangements have been employed in which the force/stroke curve of a cased type rotary solenoid may be modified or adjusted, including the arrangements shown in the patent of Smith, U.S. Pat. No. 3,027,772 issued Apr. 3, 1952 in which detents are provided at the deep ends of the ball races for the purpose of permitting a decrease in the current necessary to maintain the solenoid in its energized position. However, the arrangement shown in the Smith patent does not provide a trip solenoid function, since it is necessary to keep some current flowing through the coil to hold the solenoid in the moved position. No permanent magnet arrangement is shown in Smith for holding the solenoid in its energized position.